The IEEE 802.22 for wireless regional area networks (WRANS) is designed to operate in the TV broadcast bands, while ensuring that harmful interference does not occur with incumbent services, e.g., digital and analog TV broadcasts, and low power licensed devices such as wireless microphones. IEEE 802.22 defines a standard for each of three channel bandwidths, namely: 6 MHz based channels; 7 MHz based channels; and, 8 MHz based channels. For each of the respective channel bandwidths the 802.22 standard defines different: subcarrier spacing and FFT/IFFT period values based on sampling frequency; symbol duration for different cyclic prefix options; OFDM parameters; and WRAN frame parameters. The use of the respective channel bandwidths is regionalized, and a universal standard does not exist.
Table 1 shows the IEEE 802.22 subcarrier spacing and FFT/IFFT period values for the three different channel bandwidths based on a sampling frequency equivalent to 8/7 of the channel bandwidth.
TABLE 16 MHz basedchannels7 MHz based channels8 MHz based channelsBasic sampling6 * 8/7 = 6.8571437 * 8/7 = 88 * 8/7 = 9.144857frequency (MHz)Inter-carrier spacing,(6 × 106 * 8/7)/2048 ≈(7 × 106 * 8/7)/2048 =(8 × 106 * 8/7)/2048 ≈ΔF (Hz)3348.2143906.254464.286FFT/IFFT period,≈298.666 . . .=256.000=224.000TFFT (μs) = 1/ΔFTime Unit (ns)1000/(6 × 106 * 8/7) =1000/(7 × 106 * 8/7) = 1251000/(8 × 106 * 8/7) =TU = TFFT/2048145.833 . . .109.375
Table 2 shows the IEEE 802.22 symbol duration for different cyclic prefixes and bandwidth options.
TABLE 2CP =CP =CP = TFFT/32CP = TFFT/16TFFT/8TFFT/4TSYM =6 MHz308.000317.333336.000373.333TFFT +7 MHz264.000272.000288.000320.000TCP8 MHz231.000238.000252.000280.000(μs)
Table 3 shows IEEE 802.22 OFDM parameters for the three channel bandwidths of 2K FFT mandatory mode.
TABLE 3TV channelbandwidth(MHz)678Total no. of sub-carriers,2048NFFTNo. of guard sub-carriers,368 (184, 1, 183)NG (L, DC, R)No. of used sub-carriers,1680NT = ND + NPNo. of data sub-carriers,1440NDNo. of pilot sub-carriers, NP 240Signal bandwidth (MHz)5.6256.5667.504
Table 4 shows the IEEE 802.22 WRAN frame parameters for the three channel bandwidths.
TABLE 4Transmit-receiveReceive-transmitCyclicNumber of symbolsturnaround gap2turnaround gap3Prefixper frame1(TTG)(RTG)BWP6 MHz7 MHz8 MHz6 MHz7 MHz8 MHz6 MHz7 MHz8 MHz1/4263034210 μs83.33 μs  190 μs270 μs1/8283338210 μs307 μs174 μs158 μs1/16303540210 μs158 μs174 μs186 μs1/32313641210 μs111 μs174 μs221 μs
These three different channel bandwidths and their respective parameters place an onerous burden on transmitter and receiver manufacturers who wish to market internationally because a differently configured transmitter/receiver must be designed, manufactured and distributed for each of the three bandwidths. This not only complicates design, manufacturing and distribution, it also contributes to consumer cost and prohibits device migration between regions that use different channel bandwidths.
There therefore exists a need for a universal transmitter and a universal receiver for the international television bands and a WRAN standard that will coexist with any know television technology (NTSC, PAL, SECAM, ATSC-8VSB, DVB-T, etc.) while enabling transmission at any one of the 6 MHz, 7 MHz or 8 MHz channel bandwidths.